CITRUS VIRUSES have b~e n the subject of an increasing number of publications during recent years. So far as the writers know, however, there is no mention of electron microscopically detectable particles representing these viruses, with the exception perhaps of the report that psorosis virus is spherical ( 10) .Electron microscopical studies on tristeza have been carried out in the Virus Department of the Instituto Agronomic0 de Campinas for more than two years. This paper reports the finding of a thread-like particle in tristeza-infected citrus plants and evidence that the thread-like particle is tristeza virus. Preliminary results have been published elsewhere (12).
O vírus do mosaico do quenopódio foi purificado por meio de centrifugações alternadas de baixa e alta velocidade, complementadas pelo tratamento com clorofórmio e álcool amílico. Foram obtidas preparações altamente ativas, que apresentaram as reações características das proteínas e um espectro de absorção da luz ultravioleta igual ao das nucleoproteínas, e que não apresentavam o fenômeno de anisotropia de fluxo. O sedimento dessas preparações purificadas, obtido na ultracentrífuga, retomado em um pequeno volume de solução de sulfato de amônio 0,2 saturada e guardado a 4°C, produz um grande número de microcristais. As partículas que compõem as preparações examinadas ao microscópio são de aspecto e dimensões bastante uniformes; são "esféricas" e de cerca de 30 milimicros de diâmetro. O material purificado se assemelha ao vírus do mosaico "southern bean", quanto ao aspecto dos cristais, mas os testes de hospedeiros e sorológicos indicaram tratar-se de dois vírus perfeitamente distintos.
A T r s M m s to purify tristeza virus were begun in 1958. Several methods, principally that of Fulton (2, 3 ) which is based on adsorption on hydrated calcium phosphate, were tried without apparent success. Other methods, including preclarification treatment of the juice by treating it with n-butanol or a mixture of ether and carbon tetrachloride ( 7 ) , were tried subsequently with better results. This paper presents the results of some of these subsequent attempts to purify tristeza virus from the juice of three species of citrus.
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